Why do objects moving at the speed of light appear smaller?

[Glynis]

If the outer galaxies are mobing at the speed of light, why aren`t they infinetly big? Also sub atomic particles which are accelerated to the speed of light are not infinitley big. Is this because sub-atomic particles behave differently to macro atomic objects?
Thanks,
Glynis

 

[Hootenanny]

Could you perhaps point me to your source which suggests galaxies and sub atomic particles travel at C? I presume by 'infinitely big' you mean 'infinitely massive'.

 

[Glynis]

Private tuition from a Bio-Physicist and also by reading Stephen Hawking. And I am therefore of the understanding that this is the reason we cannot exceed the speed of light. And you are correct, I mean infinitely massive.
Thanks,
Glynis

 

[Hootenanny]

An object with a finite (non-zero) invariant mass cannot travel at C. A good lay explanation is given by Dr. John Simonetti of the Department of Physics at Virginia Tech;

Einstein's Special Theory of Relativity is the key to understanding this particular question. Any reference on the subject (and I'm sure there are loads of them written for a wide range of students) will have some discussion on this. Briefly, to make an object accelerate from rest to any speed, we must expend some energy (by using a rocket engine, say). For low speeds (much less than the speed of light --- 186,000 miles per second; all all humans have traveled only at very slow speeds compared to that of light), an increase in the energy expended results in a reasonable increase in the speed of the object. However, as the SR theory says, when the object is traveling at very large speeds (= a considerable fraction of the speed of light), then an additional expenditure of energy will not result in as large an increase in speed as it would have at lower speeds. In other words, we have to expend quite a bit of energy to increase the speed by only a little bit, if the rocket ship is already traveling fast. If the rocket ship is traveling at 95% of the speed of light, a tremendous amount of energy will be necessary to make it travel at 96% the speed of light. In trying to make it travel at the speed of light, we would need to expend an infinite amount of energy --- in other words, we can't make it travel at the speed of light.

I do hope that your Bio-Physicist didn't say that it is possible for such particles to travel at C.

 

[Danger]

And as for the galaxies, they are not moving at relativistic speeds within the space that they occupy. The space itself is expanding away from us. That does not violate Relativity.

 

[LURCH]

Particles in particle accelerators do travel at speeds that come quite close to the speed of light. As a result, their mass is thousands of times greater than when they are at rest.

The detection chambers in these accelerators are specifically set up with this in mind, monitoring the space through which the particles will travel, given their much greater mass, as opposed to the space through which they would travel at their normal mass. The increase in mass that is observed in these particles is consistent with the predictions of GR, which also predict that their mass would become infinite if they reached light speed.

 

[pervect]

Cosmologists use coordinate systems that aren't compatible with SR. So while cosmologists do talk about speeds that area faster than light, these aren't the same sort of "speeds" that we talk about in special relativity. Saying that "space expands" is one way of trying to describe the difference - a possibly more accurate but abstract explanation requires a lot of discussion of coordinate systems and their properties, and why cosmologists use a coordinate system that is convenient for them but not compatible with special relativity.

 

[Glynis]

Could the infinitely massive factor when traveling at C be used to suggest omniprescence and allow a ship to reach different parts of the universe almost simultaneously?

Does the factor of infinitely massive when traveling a C take into account a universe limited in size. For if space is still expanding then it is not yet infinite.

 

[Jheriko]

With galaxies it is important to remember that the expansion of space is "metric expansion" i.e. the space-time itself is expanding. This allows objects to appear to move faster than c from our perspective. They do not exceed c, however, since the distance itself has expanded.

If you imagine two spheres resting on an expanding sheet of rubber, they can both be at rest relative to the rubber, but appear to be moving apart at a rapid pace. If they are close enough together then they "share" a depression and the expansion needs to be strong enough to pull them apart, otherwise they remain in the same place.

The only reason everything does not "explode" is because it is bound gravitationally, electrostatically, with nuclear forces etc..

There are other relativistic situations where objects appear to exceed the speed of light relative to one observer, in all of these cases though these objects to not exceed the speed of light locally. This is due to the curvature of space.

Also remember, objects traveling at c must be massless. Massive objects will be limited to < c and will always maintain a finite relativistic mass. Instead of considering relativistic mass you should be thinking in terms of invariant mass anyway. Relativistic mass is a concept which has caused as many problems as it solves. It is not "really real", i.e. it works for making some relativistic equations agree with classical theory, but not for all. Most importantly it breaks F = ma.

I suggest you read this page: http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.html

 

[lightarrow]

Could the infinitely massive factor when traveling at C be used to suggest omniprescence and allow a ship to reach different parts of the universe almost simultaneously?

If your question where "...when traveling almost at c..." then the answer would have been yes. You could travel for a few seconds and reach distant galaxies, for example. But, coming back on Earth you would find millions or billions of years has passed there (maybe Earth and solar system wouldn't exist anylonger).

 

[quantum123]

You just need to turn your head 180 degrees and you will see the stars turn around you at speed >> c with respect to your frame of reference.

 

[Glynis]

If there is an aspect of sound emanating from the big bang, as I have heard there is and it is universal then this medium could be used for travel and be combined with the factor of omnipresence or universiality of traveling at C. Also if time-space is curved then we could define these guages closer, analyse their behaviour; engage other gravitational factors and bend time so that no time discrepancy in traveling at C would take place and I did say previously the factor of traveling at C not the actuality.

We would need to have a universal not individually progressive time measurement unit and do things like start ships
from a past time energy field. This, of course, would need careful and precise calculation involving heat, time sound and gravity guages.

I would suggest the ensuing crude equation to enable us to extricate a suitable applicable time measurement for throughout the universe:

Infinite non-actual mass defined at a specific date, as the definition no longer applies at the present. Yet it is a constant. It
is defined but can never be given or defined size-wise as an absolute
___________________________________________________________________________________________________________
Actual mass of ship at 30 mph

equals a time definition.Being infinite cannot be defined, as what is infinite must change with the continuing accommodation of more space and time and what was infinite two hours ago is no longer infinite. However the factor infinite follows the expansion of the universe constantly but changes its guages phenominally quickly.
Jheriko: please explain F=ma in longhand for me

 

[Littlepig]

Particles in particle accelerators do travel at speeds that come quite close to the speed of light. As a result, their mass is thousands of times greater than when they are at rest.

why? by m=m'*Y?? if that's so, that mass is relativistic right?? another question: is that mass "seems" normal?? or if we look at it, it has really increased??

 

[Chris Hillman]

Suggested reading

Hi, Glynis,

If there is an aspect of sound emanating from the big bang, as I have heard there is...

Do I understand you to say that you think the Big Bang made an audible sound, as in sound waves? There would be several confusions there, including:

1. the so-called "Big Bang theory" is a bit of a misnomer, since it really says that the universe was once much denser and hotter than it is now, and has been expanding and cooling ever since, somewhat like what might happen after a kind of explosion in deep space,

2. while the idea of an explosion suggests the right idea in some respects, you shouldn't think of this as having occurred in some particular location,

3. sound cannot propagate through the near vacuum of interstellar space.

Private tuition from a Bio-Physicist and also by reading Stephen Hawking.

I'd suggest you put away the popular book by Stephen Hawking and try instead the popular book by Steven Weinberg which I recommend on this page: http://www.math.ucr.edu/home/baez/RelWWW/reading.html#pop
This book directly addresses your confusion about the motion of "galaxies at the limits of observable universe", so to speak.

 

[DocN]

Perhaps, not travel at "c" not greater than "c"--Einstein's theory doesn't object to this--objects could travel at speeds greater than "c" but not slower than "c".
Doc

 

[Chris Hillman]

Tachyons again

Hi, DocN,

Perhaps, not travel at "c" not greater than "c"--Einstein's theory doesn't object to this--objects could travel at speeds greater than "c" but not slower than "c".
Doc

I think you're referring here to the notion of a tachyon, and we've just been through the reasons why this speculative notion appears to have no experimental support and is dubious for various theoretical reasons.

The original question seemed to concern something completely different, a misconception about "Big Bang" cosmological models.

 

[DocN]

Can you find some equation of Einstein that would prohibit some particle from always traveling faster than "c" (speed of light)?
Doc

 

[Chris Hillman]

I think you misunderstood what I wrote. I know what you are talking about, and don't disagree with that, but there are further issues to consider in discussing whether or not we should seriously expect to ever observe any tachyons.

 

[DocN]

Hi,
I was not thinking of tachyons but any disagreements to Einstein's SRT equations. Although such a particle (s>c) would have to always travel greater than c, never lower.
Doc

 

[Chris Hillman]

Which is the basic idea behing the tachyon proposal. I don't understand what the problem is here.

 

[IamAmenRa]

It appears this thread has gone off on a tangent. Here is a question similar to Glynis' question that might also ask the same question. Einstein says as you approach light speed you become infinitely massive. My question, why aren't light particles infinitely massive? Perhaps if you answer this question, it is the same answer to Glynis' original question.

 

[Lost in Space]

If light is extremely redshifted for early galaxies, could it be that light has been so redshifted that even earlier (and distant) galaxies are no longer visible? And if so, is there any way we could still detect these from other wavelengths of light (shorter or longer).

 

[Quinzio]

You just need to turn your head 180 degrees and you will see the stars turn around you at speed >> c with respect to your frame of reference.

When you turn your head, almost each atom of it has a different inertial frame. :uhh: